1. Field of the Invention
The present invention generally relates to an apparatus and method for performing Hybrid Automatic Repeat reQuest (HARQ) in a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for HARQ signaling when fixed resource allocation is carried out in a broadband wireless communication system.
2. Description of the Related Art
In a next generation communication system, also known as a 4th Generation (4G) communication system, researches are actively in progress to provide users with services with various Quality of Service (QoS) requirements at a data transfer speed of about 100 Mbps (Megabits per second). In particular, the 4 G communication system is currently being developed to ensure mobility and QoS in a Broadband Wireless Access (BWA) communication system, such as a wireless Local Area Network (LAN) system, a wireless Metropolitan Area Network (MAN) system, etc. Examples of such a communication system include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system, an IEEE 802.20 communication system, etc.
An IEEE 802.16 communication system and an IEEE 802.20 communication system use an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme. In addition, an IEEE 802.20 communication system supports a scheme in which a wireless resource is fixedly allocated to a specific Mobile Station (MS), and this scheme will be referred to herein as a fixed resource allocation scheme or fixed allocation. It is expected that future IEEE 802.16m communication systems will also support the fixed resource allocation scheme.
The fixed resource allocation scheme reduces overhead that occurs when resource allocation information (or a resource allocation message) is transmitted to an MS for each frame. That is, a Base Station (BS) periodically allocates specific resources to the MS in a fixed manner while the MS receives a service that periodically generates traffic. Thereafter, the MS performs communication by continuously using the fixed allocated resources without having to verify the resource allocation information until the fixed allocated resources are modified or released. Therefore, the BS does not have to transmit the resource allocation information to the MS for each frame.
However, when a Hybrid Automatic Repeat reQuest (HARQ) packet is transmitted by using the fixed allocated resources, packet loss and delay may occur due to an erroneous response signal for the HARQ packet.
For example, assume that an MS is successfully received a HARQ packet and thus transmits an ACKnowledgement (ACK) signal as a response signal, but a BS recognizes a Non-ACKnowledgement (NACK) signal as the response signal due to errors.
In this case, since the MS has successfully received the pervious packet, the MS deletes the previous packet from a receiving buffer, and then waits for a new packet. However, since the BS has recognized the NACK signal as the response signal, the BS retransmits the previous packet, which leads to unnecessary packet retransmission. In addition, since the MS regards a currently received packet as the new packet and does not perform symbol-combining, there is an increasing possibility of unsuccessful packet reception. If packet reception has failed, the MS transmits the NACK signal as the response signal, and the BS retransmits the previous packet. As such, the BS retransmits the packet several times even when the packet has already been successfully received by the MS, resulting in waste of wireless resources.
For another example, assume that an MS fails to receive a HARQ packet and thus transmits a NACK signal as a response signal, but a BS recognizes an ACK signal as the response signal due to errors.
In this case, since the MS fails to receive the previous packet, the MS waits for retransmission of the previous packet. However, since the BS has recognized the ACK signal as the response signal, the BS transmits a new packet to the MS. Then, the MS regards the new packet as the previous packet, and performs demodulation by symbol-combining the new packet with the previous packet stored in a receiving buffer. Since the two combined packets are different from each other, the MS determines that the packet reception has failed, and transmits the NACK signal to the BS again as the response signal. In response to the NACK signal, the BS retransmits the new packet, and the MS continues to fail in receiving the packet. As a result, the MS fails to receive both the previous packet and the new packet, and thus both of the two packets are lost. In addition, packet retransmission is repeated up to a maximum number of times, resulting in waste in wireless resources. Moreover, delay may occur when another packet is transmitted.
Accordingly, a need exists for a technique for enhancing reliability of signaling when HARQ is performed by using fixed allocated resources.